This invention relates to adjustable torque limiting apparatus and more particularly to such apparatus suited for use with sources of rotary power such as drill motors and the like.
One type of torque limiting device in common use utilizes a clutch having frictionally mated surfaces which are preloaded and designed to slip with respect to one another. Slippage occurs when a predetermined limit of torque is delivered by a power source, such as a drill motor, to the input of the device. For example, U.S. Pat. No. 3,710,591 to Gore et al. discloses a power drive clutch comprising a carrier housing, an input shaft, and a pair of elements within the housing which have mutual surfaces which are frictionally mated and spring loaded such that when a predetermined amount of torque is delivered to the input shaft the surfaces slip with respect to one another so that power is no longer delivered to the carrier housing. A drill bit or the like is selectively attached to the carrier housing for applying power to a workpiece. This type of device has a disadvantage in that the carrier housing rotates until the predetermined torque rating is exceeded. A safety hazard thus arises due to the fact that this type of tool is often used with high speed power equipment. Furthermore, the Gore et al device cannot be adjusted by the user thus precluding readjustment of the maximum torque setting for varying applications in which the device may be used.
An important use of a torque limiting device is to control the torque transmitted to a conventional self-feeding tube expander. If too much or too little torque is applied to the tube expander, a good seal between the expanded tubes and the supporting sheet is not established.